1. Field of the Invention
The present invention relates to a cutting method by sandblasting, and more specifically to a cutting method by sandblasting suitable for the cutting out of parts from a plate-shaped workpiece and the formation of a through-hole on a plate-shaped workpiece.
It should be noted that in the present invention, the term a through “hole” also refers to “groove.”
2. Description of the Related Art
In general, the following kinds of processing are performed by cutting:
cutting out (dicing) a cover glass used in a display screen of a mobile phone, cutting through thin-sheet glass for a touchscreen mounted on a liquid crystal display screen or the like, cutting out parts from a plate-shaped workpiece such as other glass, ceramic, metal, a silicon wafer, or the like, and forming a hole or groove on such a workpiece.
Examples of such cutting include cutting out or hole making performed using a grinding wheel rotating at high speed which is followed by finish processing, hole making using a carbide drill or a diamond drill, and the like.
However, these processing methods are not suitable for processing a surface to be processed having a relatively large area. Accordingly, to improve productivity, processing by sandblasting suitable for processing for a relatively large area is also performed.
In the case where the aforementioned dicing, hole making, or the like is performed by sandblasting as described above, a sandblast-resistant protective film called “a resist” which has a pattern formed on portions where cut is not to be made on a surface of the workpiece (hereinafter called “no-cut portions”) before sandblasting to protect the no-cut portions.
In the case where the number of workpieces to be processed is relatively low, a process is done by forming the resist on no-cut portions, and a resist made of a metal plate, a ceramic plate, a glass plate, a resin film or the like that has open holes or grooves corresponding to portions where cuts are to be made may be fixed or bonded to a surface of each workpiece. However, in the aforementioned case where a large number of cover glasses for mobile phones, or the like, are to be processed, a resist (photoresist) is formed on each workpiece by lithography using a photosensitive resin.
However, the aforementioned resist formation by lithography is achieved through the following steps of:
attaching photosensitive resin to the entire front surface of a workpiece by an operation such as laminating the entire front surface of the workpiece with a photosensitive resin film; placing a photomask in which openings corresponding to an exposure pattern are formed, on the photosensitive resin; then irradiating the photosensitive resin with light using a light radiation device such as an ultraviolet radiation device or the like, thereby curing the photosensitive resin in portions where no cut is to be made; removing uncured portions of the photosensitive resin by an operation such as immersing the workpiece in a cleaning tank; and thereafter drying the workpiece using a dryer.
As described above, in resist formation by lithography, photosensitive resin is attached to the entire workpiece, and then unexposed portions are cleaned with washing water and discarded together with the washing water. Accordingly, the amount of use of photosensitive resin which is discarded without being used as a resist is large. Thus, the above-described resist formation by lithography does not efficiently use resources, and is not economical.
Also, resist formation by the aforementioned method requires the placing of a photomask, a large light radiation device for exposing an entire surface of a workpiece to light, cleaning after the exposure for removing unnecessary resin, a drying step after the cleaning, and the like. Accordingly, a large number of steps are needed to obtain a sandblast-resistant resist. Further, it is also necessary to prepare equipment for enabling these steps, such as a device for placing a photomask, a light source, a cleaning tank, and a dryer, and to ensure a wide installation place for installing these. Thus, a lot of initial investments are needed.
In order to solve such problems in photoresist formation by photolithography, one method for forming a resist without using photolithography has been proposed in which ink containing an alkali-soluble curable resin is dispensed to a surface of a workpiece in accordance with a pattern of no-cut portions by inkjet printing, and cured to form a sandblast-resistant resist (Japanese Patent Application Laid-Open No. 2008-265224).
In the method described in the aforementioned '265224, ink containing an alkali-soluble curable resin is deposited only on required portions on a workpiece by inkjet printing. Accordingly, excess resin is not used in resist formation. Further, the placing of a photomask, cleaning for removing unexposed excess resin, and drying after the cleaning are not needed. As a result, the number of steps for obtaining a sandblast-resistant resist can be greatly reduced, and a device for placing a photomask and a cleaning tank become unnecessary with the reduction in the number of steps. Also, a light radiation device and the like can also be miniaturized. Thus, the advantage can be obtained that initial investments and the like can be made low.
However, a sandblast-resistant resist needs to have strength enough to remain on a surface of a workpiece and thus to protect the surface of the workpiece from a cut by abrasive until cutting on the workpiece is finished even when abrasive collides against the workpiece at high speed.
Further, for obtaining such sandblast resistance, the invention described in the aforementioned '265224 has limitation on the physical properties and the like of ink to be used to obtain a sandblast-resistant resist. Specifically, the invention uses an alkali-soluble curable resin having a weight-average molecular weight within a predetermined range (Japanese Patent Application Laid-Open No. 2008-265224, paragraph [0023]), for example. Furthermore, in order to obtain sandblast resistance, a large thickness of a resist film is required. In the case where a needed thickness of the resist film cannot be obtained in a single application, ink is applied over a plurality of times (as above '265224, [0023]). Due to this and the like, resist formation takes a long time.
It should be noted that the following problem arises which is common to the method described in the above '265224 and the case where a resist is formed by lithography:
in the case where processing such as cutting out or hole making is performed by sandblasting, though an entire portion not coated with resist is evenly cut in the initial phase of the processing as shown in FIG. 3A, the shape of the cut hole gradually changes, with increasing cut depth, into the shape of a wedge which is deepest at a central portion (FIG. 3B); as the projection of abrasive is further continued to increase the cut depth, abrasive which has entered the cut hole turns around at a bottom portion of the cut hole to scrape away the side surface of the cut hole when being discharged to the outside of the cut hole, and may increase the diameter of the hole to such an extent that the hole reaches a portion under the resist; when the cut is continued until the cut depth is further increased to penetrate the thickness of the workpiece, since the thickness of the workpiece is penetrated at the center of the bottom portion of the cut hole, the side surface of the cut hole has a shape inclined with respect to the front and back surfaces of the workpiece as shown in FIG. 3D, and finish processing is therefore needed.
Also, as described with reference to FIGS. 3A to 3D, it is difficult to form a fine through-hole with high accuracy.
Further, in such cutting by blasting, further improving processability by shortening processing time provides convenience.
Accordingly, the present invention has been made to overcome disadvantages of the above-described prior art, and an object of the present invention is to provide a cutting method by sandblasting in which a resist is formed by inkjet printing to maintain advantages, such as a reduction in the amount of use of resist ink and the simplification of a facility, of the invention described in the aforementioned '265224, and by which necessary sandblast resistance can be obtained even in the case where conditions, such as average molecular weight described in the abovementioned '265224 as being necessary, on physical properties of resin to be used are relaxed or where the film thickness of a resist is reduced.
Another object of the present invention is to provide a cutting method by sandblasting in which even a fine hole or slit can be accurately formed by preventing or relaxing the aforementioned problems occurring in the case where a cut is made by sandblasting, i.e., an increase in the width of a cut hole to the extent that the cut hole extends to under a portion coated with resist and an incisive state due to the inclination of the sidewall of the cut hole, and which can reduce the labor of the aforementioned finish processing such as polishing the side surface of the cut hole after the cut to a plain state.